Knee Replacement – the risks

As with any kind of major surgery, with knee replacement surgery there are potentials risks involved and there are possibly complications that you need to be aware of. The main risks from knee replacement surgery are infection ,deep vein thrombosis or neurovascular damage. Also, with time the replacement joint may potentially wear out and require another replacement (a revision knee replacement).

Knee replacement surgery is fairly major surgery, and as is the case with any major procedure, there are various potential complications that can occur. Probably the biggest worry that is at the forefront of most people’s minds is the risk of infection. Bacteria exist all around us; in our skin, in the air and even sometimes in our blood. Bacteria can sometimes stick to the metal surface of a knee replacement, where they can multiply. They can then form a sticky membrane around themselves that makes it difficult for antibiotics to get to them. Superficial infections near the surface of a wound are more common and can normally be treated effectively with a simple course of antibiotics. However, deep infections affecting the joint itself are far harder to treat, and sometime it becomes necessary to remove the entire artificial knee joint, leaving the joint fused straight.

For the above reasons, the risk of infection is taken very seriously in TKR, especially with the prevalence of new antibiotic resistant strains of bacteria, such as MRSA. Patients are therefore given 1 dose of prophylactic antibiotics before the surgery, followed by 2 doses postoperatively. Furthermore, the procedure is carried out under full aseptic conditions, in a theatre with ultra-filtered air that is carefully controlled using a laminar airflow environment.

The risk of infection is considerably lower in the private sector than it is in the NHS. However, it should be stressed that this does not necessarily reflect better surgical or nursing care, or cleaner hospitals, and it may potentially simply be a reflection of the more complex cases and sicker patients that generally tend to be treated within NHS hospitals, with the inherent greater risk of infection that this carries.

One of the other main potential complications that is associated with joint replacement is the formation of deep vein thromboses (DVTs). DVTs can develop in the veins of any limb that remains static for too long. The risk of thrombosis also increases due to the stress hormones that are released after any kind of major surgery. Small DVTs, below the level of the knee, are frequent and can often cause no actual symptoms. However, larger DVTs, especially those that develop above the level of the knee can actually cause painful swelling in the leg, and they can break off and pass into the circulation and potentially lodge in the lungs (a pulmonary embolus) – which can on rare occasions be fatal.

Again, therefore, this potential complication is also taken very seriously and to try and reduce the risk patients are given low-molecular-weight heparin injections once a day after the surgery, which slightly thins the blood, reducing the potential for clots to form. In addition, patients are mobilized as early as possible postoperatively, and are encouraged to repeatedly exercise and contract the calf muscles in order to pump blood and keep it moving through the veins of the leg.

All of the main nerve and blood vessels around the knee are around the back of the joint. With knee replacement surgery, the incision is made at the front of the knee. Therefore, thankfully, the risk of potentially damaging any significant nerves or blood vessels at the time of knee replacement surgery is only tiny.

Natural knee joints are made of living tissue that is constantly in a cycle of repairing and rebuilding itself. Knee replacements, however, use metals and plastics – all of which can wear out with time. A worn or loose knee replacement often causes significant pain, and if the loosening is sufficiently severe, then the TKR may need to be removed, and a new knee inserted (a revision knee replacement).

Revision TKRs are technically more difficult procedures, with a greater risk of blood loss, and with perhaps twice the potential complications of a standard primary TKR. Furthermore, the longevity of a revision TKR is less than it is for a primary TKR, meaning that the revision TKR may not actually last as long as the first one did.